This invention relates both to air duct inlet silencers and to air duct outlet silencers, in particular to silencers designed for use with gas turbines.
Stationary gas turbines for the production of power are well known for use by power producing industries. One difficulty that is encountered with the use of gas turbines is the noise that they can create during their operation. Because of this noise, efforts have been made in the past to provide sound attenuators or sound reducing devices both at the intake of the gas turbine and at the outlet end. However for various reasons problems have been encountered in developing satisfactory inlet silencing units and outlet silencing devices for these gas turbines. One reason for these difficulties is that the flow into and out of stationary gas turbines is often compromised because of spacial constraints and cost factors. Many such systems feature a short plenum box with a vertical inflow into the compressor of the turbine and an axial outflow. In the usual case, inlet silencers are installed ahead of the plenum while the gas turbine outlet is often dumped into a plenum which feeds a vertical exhaust section consisting of some form of silencer and exhaust stack.
Outside of the field of gas turbines, both air duct inlet silencers and air duct outlet silencers have been developed in recent years for use in combination with axial fans providing air to large structures such as office buildings and industrial buildings. For example U.S. Pat. No. 5,587,563 issued Dec. 24, 1996 to Dipti K. R. Datta describes both an air inlet silencer for an axial fan and an air outlet silencer, both of which employ sound attenuating material located behind perforated sheet metal walls. The duct inlet silencer includes an exterior housing that has two principal air inlets located on opposite sides of the housing. The unit also has a single air outlet located at one end of the housing. The two inlets and the outlet are connected by airflow passageways defined by interior walls and these passageways bend 90 degrees from the inlets to the outlet. Sections of the interior walls are made from the aforementioned perforated sheet metal. In one preferred embodiment the passageway from each inlet is divided into four quadrants with upper and lower quadrants separated by a horizontal divider.
With respect to the fan outlet silencer described in the aforementioned U.S. patent, it has a top, bottom, and side walls and between these walls extend first and second series of splitters with the splitters of each series being spaced apart to form smaller air passageways. The splitters of each series are mounted side by side in a row and the splitters of one series are staggered with respect to the splitters of the other series in a direction transverse to the direction of airflow. The sound attenuating material that is used in both the inlet silencer and the outlet silencer for an axial fan as described in this U.S. patent is standard sound attenuating material such as fibreglass bats stuffed between the interior walls and the exterior walls and into the interior of the splitters.
Up to the present time, there has been no suggestion that inlet and outlet silencers of this general type could be used in combination with relatively large, stationary gas turbines. One difficulty with the known outlet silencers designed for use with ordinary axial fans is that they are not able to withstand the high temperatures that exist in the hot air stream emitted by the gas turbine nor are they able to withstand the much higher air velocities which can be as much as 15000 feet/minute and higher.
In the air handling art wherein systems have been developed for providing fresh air and return air to structures using suitable fans, it is known that turning vanes to redirect the direction of the airflow into or out of a fan unit can provide excellent turning performance including uniform airflow with minimum pressure loss. The use of such turning vanes in combination with sound attenuating material has proven to be effective in air supplying and air conditioning applications involving the use of axial fan units. Most of these systems employ conventional acoustic dissipative media such as fibreglass. In many of these recently developed systems the sound absorbing surface comprises a special sandwich construction consisting of a perforated cover sheet, an erosion resistant duct-liner and bulk fibre located behind the duct liner and packed to the proper density. However as far as applicant is aware, this sound attenuating technology has not been used with nor proposed for use with gas turbines such as large, stationary gas turbines used for the production of power.
It is an object of the present invention to provide a novel air duct inlet silencing apparatus for use with a stationary gas turbine, this apparatus having substantial sound reducing capabilities and being reliable and relatively easy to maintain over the life of the inlet silencer.
It is another object of the present invention to provide a novel sound attenuating duct unit suitable for connection to the outlet of a stationary gas turbine, this unit being relatively inexpensive to manufacture while having substantial sound attenuating capabilities.
According to one aspect of the invention, an air duct inlet silencing apparatus for use with a stationary gas turbine includes an inlet duct structure extending around a first vertical axis and extending vertically along this first axis, the duct structure having an upper duct section with a plurality of vertically extending sides and a top cover. Air inlet openings are formed in at least two of the vertically extending sides and an air outlet is formed at the bottom end of the structure. The air outlet is adapted for connection to an air intake of the gas turbine. There is also an elongate, centrally located, airflow defining member which extends around a vertical primary axis and extends downwardly from the top cover, past the air inlet openings, and along the primary axis. This airflow defining member is formed with a perforated sheet metal exterior and contains sound attenuating material. Airflow passageways extend from the air inlet openings towards the air outlet and each is defined by at least one interior wall mounted in the duct structure. Each airflow passageway bends substantially so that a lower section thereof extends substantially parallel to the vertical first axis. A substantial portion of the at least one interior wall is made of perforated sheet metal and sound attenuating material is contained in the at least one interior wall and is covered by the perforated sheet metal.
In one preferred embodiment of this inlet silencer, the upper duct section has at least four vertically extending sides and the air inlet openings are formed in all of the vertically extending sides. The preferred airflow defining member includes a substantially conical or multi-sided upper section that extends downwardly from the top cover to a substantially cylindrical or multi-sided lower portion thereof.
According to another aspect of the invention, a sound attenuating duct unit suitable for connection to an outlet of a stationary gas turbine includes a housing having a horizontal housing section and a vertical housing section and having sidewalls surrounding a main airflow passageway that extends along a substantial bend. An air inlet is located at one end of the horizontal housing section and is adapted for connection to the outlet of the gas turbine. An air outlet is located at an upper end of the vertical housing section. There are at least first and second series of splitters mounted in the housing with the splitters of each series being spaced apart to form smaller air passageways and being mounted side-by-side in a row. The second series is positioned downstream in the airflow passageway relative to the first series and is staggered relative to the first series in a direction generally transverse to the direction of airflow in the main passageway. The splitters contain sound attenuating material, such as ceramic wool, capable of withstanding airflow temperatures inside the main airflow passageway of at least 500 degrees Celsius. At least a substantial portion of both sidewalls surrounding the main airflow passageway and metal sidewalls forming the splitters are made of perforated sheet metal having a thickness of at least 12 gauge.
In a preferred embodiment of this outlet silencer for a turbine, the sound attenuating material is mineral wool and a perforated sheet metal is made of stainless steel.
According to a still further aspect of the invention, there is provided a combination of a gas turbine for installation and use at a selected stationary site and a sound attenuating duct unit connected to a hot air exhaust outlet of the gas turbine. The duct unit includes a housing having a horizontal housing section and a vertical housing section and having sidewalls surrounding a main airflow passageway that extends along a substantial bend. There is an air inlet located at one end of the horizontal housing section and connected to the exhaust outlet of the gas turbine. An air outlet is located at an upper end of the vertical housing section. The combination also includes at least first and second series of splitters mounted in the housing with the splitters of each series being spaced apart to form smaller air passageways and being mounted side-by-side in a row. The second series is positioned downstream in the airflow passageway relative the first series and is staggered relative to the first series in a direction generally transverse to the direction of airflow in the main passageway. The splitters contain sound attenuating material capable of withstanding airflow temperatures in the main airflow passageway of at least 500 degrees Celsius. Also at least a substantial portion of both the sidewalls surrounding the main airflow passageway and metal sidewalls forming the splitters are made of perforated sheet metal having a thickness of at least 12 gauge.
In a preferred embodiment of this combination each splitter includes a rounded nose portion at a leading edge and this nose portion is made of imperforate stainless steel.
According to still another aspect of the invention, an air duct silencing apparatus for use at an inlet of a stationary gas turbine comprises an inlet duct structure extending dowardly along a vertical first axis having a duct section with a plurality of vertically extending sides and a top cover, a plurality of inlet openings being located on one of the vertically extending sides, which is an open side to a substantial extent, and an air outlet being formed at a bottom of the structure. The outlet is adapted for connection to an air intake of the gas turbine. A plurality of curved airflow splitters separate the inlet openings and extend inwardly and downwardly from the inlet openings towards the air outlet. The airflow splitters each are formed with a perforated sheet metal exterior and contain sound attenuating material. A plurality of airflow passageways are formed by and between the airflow splitters and extend from the inlet openings towards the air outlet, these airflow passageways bending substantially and an elongate bottom section of each passageway extending substantially parallel to the vertical first axis.
Further features and advantages will become apparent from the following detailed description of preferred embodiments taken in conjunction with the accompanying drawings.